Apparatus and method for providing asymmetric oscillations

ABSTRACT

Disclosed is an apparatus and method for providing asymmetric oscillations to a container. The container may include a fluid, a particle, and/or a gas. A vibration driver attached to the container provides asymmetric oscillations. A controller connected to the vibration driver controls an amplitude, frequency, and shape of the asymmetric oscillations. An amplifier amplifies the asymmetric oscillations in response to the controller. A sensor disposed on the vibration driver provides feedback to the controller.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent application is a divisional and claims the prioritybenefit of U.S. patent application Ser. No. 15/489,507 filed Apr. 17,2017, which is a continuation and claims the priority benefit of U.S.patent application Ser. No. 14/177,844 filed Feb. 11, 2014, which claimsthe priority benefit of U.S. provisional patent application No.61/763,029 filed Feb. 11, 2013, the disclosures of which areincorporated by reference herein.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention is generally related to levitating, suspending,moving, fluidizing, or mixing solid particles or fluid bubbles in afluidic environment. More specifically, the present invention is relatedto an apparatus and method for levitating, suspending, moving,fluidizing, or mixing solid particles or fluid bubbles in a fluidicenvironment by suitable non-sinusoidal vibration.

Description of the Related Art

There are several existing methods for levitating or suspendingparticles in a fluid (liquid or gas).Levitation methods include usingelectromagnetic, electrostatic, acoustic, and aerodynamic forces.Electromagnetic and electrostatic methods can only levitate materialshaving the right electromagnetic properties and cannot levitate gasbubbles within a fluid. Acoustic levitation methods work with a widerrange of material, but the material is only be levitated at specificacoustic nodes, and not dispersed throughout a volume. Aerodynamiclevitation requires a net upwards directional flow of air or other fluidto keep particles suspended, and cannot simultaneously levitate gasbubbles and solid particles within a fluid.

The suspension of multiple particles in a fluid, also calledfluidization, can also be achieved by vibration of a container or fluidat accelerations above gravity. When low frequency vibration is used,particles are imparted energy primarily through collisions with thebottom of the container or collisions with other particles. Ultrasonicvibrations transmit energy by sound waves through the bulk fluid whichcan accelerate particles and keep them suspended, or achieve a level ofhomogenization of a liquid that persists long after the vibrationsended. However, the energy required can be high if the particles arelarge or dense, and cavitation, which may be undesirable, often occurs.

Since the 1950s or earlier, it has been known that gas bubbles can belevitated in a liquid that is subjected to low frequency (about 100 Hz)vertical vibrations. The levitation is thought to be due in part to thebubble volume oscillating as it moves up and down within the liquid. Thesolutions to the force equations in the literature on this subjectpredict that a bubble will levitate at a certain height from the top ofthe liquid, depending on the oscillation frequency and other factors,but not the amplitude (as long as the amplitude of the acceleration issomewhat greater than the acceleration due to gravity). However,researchers have found that the amplitude of vibration does have someinfluence, though they have not yet explained why.

Prior researchers have made assumptions about the drag force acting onthe air bubbles (or ignored drag altogether), leading to the erroneousconclusion that the drag force itself does not affect the levitation.However, drag forces acting on the bubbles can be complicated and aregenerally not linearly related to velocity. In particular, as theamplitude of vibration is increased, the maximum velocity of the bubblescan increase into the region where drag forces are more proportional tothe square of the velocity. In other words, the bubbles had a highReynolds number. Researchers have also not considered the effect ofnon-sinusoidal vibrations, possibly because they have assumedincorrectly that the response is linear.

The current general-purpose vibration testing procedures are singlefrequency tests, swept sine tests, random tests, and drop or impulsetests. These tests are insufficient to uncover significant defects (orfeatures) which can be caused by non-linear vibration responses to somereal-world non-sinusoidal vibrations. Vibration testing can be greatlyimproved by utilizing non-sinusoidal vibrations that enhances or exposesthe non-linear vibration response. One particular industry that cangreatly benefit from improved vibration testing is the aerospaceindustry, including battery systems, on-board fuel storage and deliverysystems, and other multi-phase systems. The lack of adequate vibrationtesting has had severe results, resulting in aerospace disasters andcostly grounding of aircraft.

Current devices and methods for the research or use of cavitation have alimited ability to control the strength or likelihood of cavitationindependent of the other effects of vibration. Typically, an ultrasonictransducer driven with a single frequency is immersed in a fluid and theeffects of sonication are concentrated near the surface of thetransducer. Cavitation can be reduced or eliminated by reducing power orother parameters, reducing other desired effects of sonication. Toachieve single bubble sonoluminescence, researchers commonly levitateand stabilize a single bubble via acoustic pressure standing waves whichrequires very specific driving frequencies. Another method developedmore recently achieves stable sonoluminescence using a “water hammertube” approximately half full with liquid. Driven externally with asingle frequency, some bubbles are entrained and experience “negative”buoyancy, dropping to the bottom of the tube. This effect cannot becontrolled without changing the frequency or amplitude of thevibrations, which affects the size and sonoluminescence of the bubbles.

Current devices for approximating the effects of microgravity underEarth gravity include drop towers, parabolic flights, and clinostats.Drop towers and parabolic flights only allow short periods ofmicrogravity, up to about 20 seconds. Parabolic flights are expensiveand limited to experiments that are safe to perform on an airplane. Thebest drop towers only give a period of about 10 seconds, with only a fewrepetitions possible per day, and high decelerations at the bottom limitthe types of experiments that can be performed. Clinostats use rotationabout a horizontal axis (or random rotation) so the time-averagedacceleration due to gravity is zero. Long experiments can be performedon clinostats, but this technique only works for items which respondslowly to acceleration, such as plants.

Current medical ultrasonography devices use a single frequency andmeasure the time and amplitude of echos to form an image inside thehuman body. Although generally considered safe, some studies have foundweak, but statistically significant effects on children exposed toultrasound in the womb. As a result, the FDA has established guidelineslimiting the acoustic power using several metrics, primarily the ThermalIndex (TI), which measures the potential for tissue heating, and theMechanical Index (MI), which measures the risk of cavitation and, to alesser degree, streaming.

Embodiments of the present invention include an apparatus and method tolevitate, suspend, or mix particles or bubbles in a fluid, or to mix twoor more fluids or granular materials, using of asymmetric verticalvibrations that nullify, reverse, or enhance the effect of gravity.Embodiments of the present invention can improve chemical reactions andother processes, and make new ones possible. Embodiments of the presentinvention can also be used to position particles or counteract theeffect of residual acceleration in a microgravity environment. Oneembodiment of the present invention includes an apparatus and method forimproved vibration testing. Another embodiment of the present inventionis also an apparatus and method using vibration to improve batteries.

SUMMARY OF THE CLAIMED INVENTION

An apparatus for providing asymmetric oscillations is recited in a firstclaimed embodiment. The apparatus includes a container. A fluid and aparticle are disposed within the container. A vibration driver attachedto the container oscillates the container to impart asymmetric velocityto the particle by way of the fluid.

A second claimed embodiment recites a method of providing asymmetricoscillations on a container. The method includes the steps of disposinga fluid and a particle in the container. Asymmetrical motion is impartedon the particle through the fluid by way of a vibration driver attachedto the container. Non-linear drag force is leveraged on the particle.

Further scope of applicability of the present invention will be setforth in part in the detailed description to follow. Taken inconjunction with the accompanying drawings and the knowledge of one ofordinary skill in the art, various advantages may be realized andattained by means of the instrumentalities and combinations, includingthose set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated into and form a part of thespecification. The drawings illustrate one or more embodiments of thepresent invention. Together with the description, the drawings serve toexplain various aspects of the invention. The drawings are only for thepurpose of illustrating one or more embodiments and not for the purposeof limiting the invention.

FIG. 1 is a side view of an embodiment of the present invention;

FIG. 2 is an illustration of the velocity of a particle inside afluid-filled vibrating container accelerated with an ideal rectangularwave; and

FIG. 3 is an illustration of a waveform that is the sum of twosinusoidal waveforms, approximating a rectangular wave.

DETAILED DESCRIPTION

Embodiments of the present invention are related to an apparatus andmethod for levitating, suspending, moving, fluidizing, or mixing solidparticles or fluid bubbles in a fluidic environment, and specifically toan apparatus and method for levitating, suspending, moving, fluidizing,or mixing solid particles or fluid bubbles in a fluidic environment bysuitable non-sinusoidal vibration.

Embodiments of the present invention also relate to an apparatus andmethod for vibration testing, particularly testing of systems involvinga fluidic environment having solid or fluid particles as well as anapparatus and method to create cavitation at a wide range of vibrationfrequencies, pressures, and bubble sizes, than has been possible withprior art, and control, increase, reduce, or eliminate cavitation atboth low and high frequencies, while controlling, increasing, reducing,or eliminating other effects of vibration.

Embodiments of the present invention also relate to an apparatus andmethod that allow for improved research into the phenomenon ofcavitation and the possibility of bubble fusion; an apparatus and methodfor testing the effects of microgravity or partial gravity within anenvironment subject to a possibly different inertial force; an apparatusand method to study, improve, control, and model crystallization,solidification (e.g., of alloys and glasses), peptization, flocculation,gelation, the sol-gel process, polymerization, foaming, acousticstreaming, mass transfer, reaction rates, and similar processes, throughnon-sinusoidal vibrations, particularly at low frequencies; an apparatusand method to increase the current that a battery can supply, or thecharging speed of a battery, through the application of sinusoidal ornon-sinusoidal vibrations; and an apparatus and method to improve andstudy ultrasound, including medical ultrasound, by controlling,reducing, increasing, or eliminating cavitation, streaming, and otherdesired or undesired effects as well as controlling, reducing,increasing, or eliminating convection and improving combustion.

As used throughout the specification and claims, the terms vibrationsand oscillations are used interchangeably. The term particle caninclude, but is not limited to a bubble, for example, an air bubble or agas bubble or a liquid bubble, a solid portion of matter having anyshape including but not limited to spherical, conical, cylindrical,cubical, combinations thereof and the like. The term fluid is defined asany substance that has no fixed shape, for example, a liquid or a gas ora combination of a liquid and gas.

FIG. 1 illustrates an embodiment of the invention that includescontainer 1 having the fluids that are mixed, or the fluid and theparticles that are levitated within the fluid, or multiple fluids andparticles. Particles are typically on the order of a millimeter indiameter but they can be as small as a molecule, or much larger than amillimeter in diameter. There is no limit to the size of the particle,if an apparatus can be built big enough to vibrate over a large enoughdistance.

Brace 2 attaches container 1 to vibration driver 3. Power amplifier 4amplifies the drive waveform from microcontroller 5 to power vibrationtransducer 3. Accelerometer 6 4 provides acceleration feedback tomicrocontroller 5 which can then modify the drive waveform in responseto the feedback. In one embodiment, microcontroller 5 uses Fourieranalysis of the signal from accelerometer 6 to determine how to adjustthe drive waveform to achieve the desired vibration. If desired,microcontroller 5 outputs data to another microcontroller or computer(not shown) monitoring the process. If flexibility is not needed, once asuitable drive waveform is found, the microcontroller 5 andaccelerometer 6 can be replaced with any device that can output arepeating electronic waveform. In addition to, or in the alternative, toaccelerometer 6, there can be other observation or feedback mechanismssuch as acoustical, optical, electromagnetic, physical, or chemicalsensors. For example, an optical sensor or camera can determine ifopaque particles are being levitated, and electrically-charged probesinside the container can detect when particles which can hold anelectric charge touch the probes. Acoustic (vibration) transducers,which generally have a higher frequency response than accelerometers,are often the best sensors for detecting cavitation collapse.

Container 1 can be of many different types, shapes, and materials. Itcan be a closed container, for batch-type operation, or connected to alarger system through connectors or valves for operation in a continuousor semi-continuous mode. In one embodiment, the sides of container 1 arevertical and the top and bottom are flat, but other shapes are possibleand may be preferred, causing different mixing patterns, themagnification of motion, or the stabilization of particles or bubbles,among other effects.

Vibration transducer 3 can be a regular audio speaker driver, a linearmotor, a rotary motor with circular motion converted to linear motionusing gears, linkages, cams, or other mechanisms, or any other devicecapable of large and fast enough vibrations. If flexibility is desired,a transducer with a wide frequency range is preferred. If the apparatusis to be used for a specific purpose that does not require flexibilityin the waveform, then one embodiment of the invention can incorporate avibration transducer designed to produce asymmetric accelerationsefficiently, through appropriate mechanisms, such as asymmetric springs,cams, or other mechanisms, or the combination of two or moreharmonically-related sinusoidal oscillators. In one non-limitingexample, a speaker driver with a spider and surround is used and acts asan asymmetric spring mechanism, with a higher spring constant in thebottom portion of the motion than the top portion. A second example of avibration driver is a circular motor with a cam designed to give higheracceleration for a shorter period and lower acceleration for a longerperiod. A third example of a vibration transducer is the combination oftwo piezoelectric oscillators, one oscillating with a frequency twicethe other with half the amplitude of acceleration, with the correctphase relationship (the maxima of the acceleration of the higherfrequency oscillator aligned with the maxima and zeros of thelower-frequency oscillator). These examples are mentioned asillustrations of some but not all embodiments of this invention.

When container 1 is vibrated at a frequency with a correspondingwavelength much longer than the container height, the fluid bulk insideis accelerated along with container 1. However, any particles within thefluid are not accelerated directly. The particles, relative to theinertial frame of container 1 and fluid, experience an accelerationopposite the exterior acceleration of container, plus (or minus) theacceleration due to gravity, plus (or minus) the acceleration due to thedrag force of the liquid on the particles. If container 1 has a constantacceleration for a long enough period, the particles reach a terminalvelocity with respect to container 1. If the acceleration is largeenough, the terminal velocity is proportional to the square root of theacceleration of container 1. The total distance traveled with respect tocontainer 1 is almost proportional to the square root of acceleration,multiplied by the time. Container 1 is then accelerated in the oppositedirection with a larger acceleration for a proportionately shorteramount of time. The particle now quickly slows down, reverses direction,and reaches a new terminal velocity. After several cycles of alternatingacceleration, the velocity and motion of the particle reaches a steadystate oscillation.

Since the terminal velocities are not linearly related to theacceleration, the average velocity is not equal to the terminal velocityunder gravity. If the higher acceleration (in the inertial frame insidethe container) is in the same direction as gravity, the ratio andmagnitude of the acceleration can be adjusted to make the averagevelocity zero, or even opposite the direction of gravity. In otherwords, the effect of gravity can be negated by the effect of thevibration, and the particle can be levitated inside the fluid.

FIG. 2 illustrates the motion of a particle within container 1accelerated with an ideal rectangular wave. The motion, relative tocontainer 1, of a particle that reaches terminal velocity in much lessthan a period of vibration similar to the solid line in FIG. 2(b). Theaverage acceleration of container 1 must equal to zero, so:

a₁t₁=a₂t₂

If the terminal velocities are proportional to the square root of theacceleration (including the acceleration due to gravity, g) then theaverage velocity can be approximated by this formula:

${averagevelocityupwards} = {\frac{k}{t_{1} + t_{2}}\left( {{t_{2}\sqrt{a_{2} - g}} - {t_{1}\sqrt{a_{1} + g}}} \right)}$

Thus, to achieve zero average velocity,

t ₂√{square root over (a ₂ −g)}=t₁√{square root over (a ₁ +g)}

Combining the equations gives

${a_{1} = {\frac{r^{2} + 1}{r - 1}g}},{{{where}\mspace{14mu} r} = {t_{2}\text{/}t_{1}}}$a₂ = a₁/r

For r=2 (i.e., the container is accelerated downwards for twice as longas upwards, at half the acceleration), the accelerations are 5 g and 2.5g.

The preceding formulae illustrates an ideal situation. In practicalsituations, the time periods are too short for terminal velocities to bereached early on in the vibration phase, or even at all, yet levitationcan still be achieved, although greater accelerations are needed.

The dashed lines in FIG. 2(b) illustrate the velocity of such aparticle. Even though the average velocity (or the total movement) is nolonger proportional to the square root of acceleration, it is still lessthan linearly related. With enough acceleration and/or a long enoughperiod, gravity can still be negated.

Similarly, a perfect rectangular acceleration wave is not practical, butthat is not an impediment to levitation. Levitation is possible evenwith an acceleration wave that is the sum of just two sinusoids, onetwice the frequency of the other and in an appropriate phase andamplitude relationship.

FIG. 3 illustrates such a waveform. Almost any waveform with a shorterperiod of stronger acceleration upwards and a longer period of weakeracceleration downwards can be used. Furthermore, the acceleration neednot even be periodic. A fluctuating waveform, with perhaps a randomcomponent, may be desired to increase the movement of the particle. Onepreferred embodiment makes use of the dual sinusoidal waveformillustrated in FIG. 3, but it is by no means the only form of vibrationthat can achieve levitation.

Particles can be denser than the fluid and be levitated upwards, or lessdense and be levitated downwards, even simultaneously. For example,experiments have levitated glass beads, thin pieces of aluminum, or finesteel shot upwards in water, while air bubbles or hollow glass bubbleswere levitated downwards. Bubble column reactors can be improved bybeing able to levitate and sink bubbles or precisely control the ratethey rise.

The acceleration needed to precisely negate gravity varies based on thesize, density, shape, and roughness of the particles, the density andviscosity of the fluid, and the shape of the acceleration waveform.Keeping everything else constant, there is a particular size particle atwhich the least acceleration is required to levitate the particle. Forexample, numerical simulations (confirmed approximately by physicaltests) can predict the preferred size for stainless steel spheres inwater, vibrated at about 30 cycles per second, with upwards accelerationtwice downwards. The preferred size of the spheres is approximately 0.05to approximately 0.3 mm, more preferably about 0.135 mm in diameter. Thepreferred size for spherical air bubbles in water under the sameconditions is approximately 0.2 to approximately 1 mm in diameter, andmore preferably about 0.5 mm in diameter; however, the air bubblesdeform under pressure so the spherical approximation is inaccurate.Particles shaped to have higher inertial drag are easier to levitate(requiring less acceleration), since they will reach terminal velocityfaster, and inertial drag will dominate over viscous drag at a lowervelocity. Thus, spheres are harder to levitate than longer, but thinner,pieces of wire of the same density and mass, and thin sheets are easierto levitate than thicker sheets.

Multiple particles can be levitated at the same time, even though theinteractions between particles complicates the process. The vibrationsor other particles may break up particles into smaller particles, whichoften makes levitation easier. For example, large air bubbles in waterbreak up from the drag force of the water, similar to the breakup oflarge raindrops falling through the atmosphere, and the smaller bubblescan be easier to levitate downwards. Bubbles of air or other fluid canalso be broken up further by solid particles (whether the solidparticles are fully levitated or not). A large number of solid particlescan be levitated and fluidized, without needing ultrasonic frequenciesor the circulating fluid that other fluidization techniques require. Theinteractions between particles can affect the amplitude of accelerationrequired to levitate the particles. Computational fluid dynamics can beused to model the effect, or the effect can be determined throughempirical research. The interactions between particles often createbeneficial side effects. For example, particles are affected by otherparticles' wakes, causing particles to “kiss” when one is upstream ofanother and close enough (e.g. within about two to three diameters forspherical particles). Particles may temporarily agglomerate, or interactin other ways. These effects can occur at relatively modestconcentrations. For example, a particle concentration of about just 1%by volume results in an average spacing of about 2.7 diameters betweenspherical particles, a distance which is close enough for inter-particleinteractions.

The agglomeration and/or “kissing” of particles can bring abouthomogeneous nucleation. Agglomeration results in local supersaturation,and “kissing” brings molecules into direct contact, both of which canhelp nucleation. Vibrations can aid in crystallization, but it is notknown if the effect can be achieved at such low frequencies asembodiments the present invention make possible. Furthermore,embodiments of the present invention increase uniformity by vibratingthe entire fluid the same amount throughout the volume of the container.Prior to or during vibrations, the fluid can be supercooled, orantisolvent can be added, or solvent can be removed, to achievesupersaturation and nucleation.

Researchers have proposed that cavitation plays a role in homogenousnucleation. However, cavitation is not necessary. Homogeneous nucleationcan be achieved by ultrasound that is of low enough power not to causecavitation. One mechanism that encourages nucleation when cavitation isnot present is inter-particle interaction brought about by the draftcaused by the velocity of the particles relative to the bulk fluid.

Cavitation

Compressible bubbles (or any portion of the container that does not forma rigid barrier) at one end of the container can cause cavitation at theopposite end of container, if the pressure drops below a certain value.This value is generally the vapor pressure of the liquid, but can varydepending on other factors such as the gas or solid content in theliquid. (Cavitation may also occur if the height of the container isclose to or larger than the wavelength of the vibration in the fluid.)Cavitation occurs when the change in liquid pressure due to theacceleration downwards (minus g) and height of liquid is greater thanthe initial pressure inside the container less (approximately) the vaporpressure of the fluid. Thus, there are several parameters which can bemodified to avoid or create cavitation, including the presence, absence,or location of bubbles, average pressure inside the container, height ofthe container, density of the fluid, and the frequency, amplitude, andshape of the vibration waveform.

Maintaining a high enough average pressure inside the container canavoid cavitation. For example, at standard atmospheric pressure, and apeak downward acceleration of about 30 g, cavitation can be avoidedwithin a container up to approximately one foot in height. Cavitationcan also be avoided at even lower pressures or higher accelerations in arigid container with no compressible bubbles or other particles, or withlarge enough compressible and expandable bubbles at both ends, as theseexisting bubbles expand with pressure changes, preventing the formationof new bubbles.

Cavitation can be easily achieved, if desired, by reducing the pressureinside the container. This reduction of pressure can be accomplishedsimply by cooling the fluid inside a sealed container, which can dropthe pressure as low as the vapor pressure of the fluid, thereby creatingbubbles of vapor or of any previously dissolved gasses. Therefore, it ispreferable to control the temperature of a rigid sealed container, andif cavitation is to be avoided, the container can be sealed at highpressure or at a temperature safely below its operating temperature.Pressure inside the container can also be controlled dynamically toprevent or enable cavitation as desired.

When the pressure is low enough for cavitation, the shape of thevibration waveform can be adjusted as described above to levitatebubbles to prevent cavitation, or the waveform can be inverted toinhibit negative buoyancy, keeping the bubbles at the top, to increasecavitation, while keeping the frequency and amplitude the same. Theshape of the bottom of the container is preferably curved or conical tostabilize the location and shape of cavitation bubbles.

Cavitation is the nucleation and collapse of bubbles (cavities) within aliquid, caused by rapid changes in pressure. Sinusoidal vibrations canbring about cavitation collapse that is even more rapid than the rate ofchange of pressure because of non-linear effects. Non-sinusoidalvibrations can increase or decrease the speed of cavitation. This can beaccomplished with the addition of higher harmonics to the vibration tocreate a wave similar to a square wave or a sawtooth wave. A square waveor the correct polarity of a sawtooth-like wave may increase the speedof cavitation, while the opposite polarity can decrease it. The bestwaveform for maximizing or minimizing the speed of cavitation collapsemay depend on many factors, including but not limited to the limitationsof the vibration driver.

A bubble can also be levitated at one vibration frequency while a secondsonic source at a faster frequency induces cavitation. The frequency ofthe second sonic source can be tuned to the bubble's natural frequency,which is a function of the bubble's size. This allows the use of a widerrange of bubble sizes and frequencies than has been possible.

The present invention is well suited for research into cavitation. Sincethe present invention can produce cavitation at low frequencies (forexample, tens of hertz or even lower), with relatively large bubbles ofa diameter exceeding a millimeter, observation and measurement of thecavitation process is much easier than with ultrasonic cavitation withmuch smaller bubbles.

Horizontal and Multidimensional Vibrations

In another embodiment of the invention, the container is vibratedhorizontally to separate or improve the mixing of particles. Forexample, a bubble column reactor can be vibrated horizontally in a waythat moves bubbles to the right and dense particles to the left,separating the bubbles from the particles, if separation is desired.When mixing is desired, the vibration can be inverted repeatedly,causing lighter and heavier particles to switch places, mixing theparticles horizontally across the entire width of the container, thusincreasing the reaction rate, mass transfer rate, heat exchange,diffusion rate, or the rates of other processes. Similarly, the shapeand/or amplitude of vertical vibrations can be fluctuated to improvevertical mixing.

Vibrations can also be applied in three dimensions simultaneously, orthe axis of vibration can be rotated. Within a microgravity environmentsuch as earth orbit, this allows full levitation of a particle and theability to counteract residual acceleration. Fluctuating the shape ofthe vibrations in three dimensions or rotating the vibration axis willmix particles in three dimensions.

An embodiment of the present invention includes vibration of an entirecontainer, instead of just one wall or the insertion of an ultrasonicprobe, the vibration is substantially uniform throughout the container.This uniformity has several advantages. Reaction speeds, temperature,concentration, and pressure may be all be more uniform throughout thecontainer.

Thermal Convection

One embodiment of the present invention can also be used to eliminate orreverse thermal convection in fluids. Vibrations of the type describedcan cause a cold layer of fluid at the bottom of the container to streamup through warmer fluid to the top of the container. This effect hasbeen demonstrated using thermochromic pigment in a liquid heated at topand cooled at the bottom. In a slow motion video, the cooler liquid roseunder the influence of the vibrations. The ability to slow or reverseconvection can improve chemical processes such as crystallization,solidification, and combustion.

The reduction or elimination of convection in gas can also be achieved.This can improve combustion processes, but, if the amplitude ofvibration is high, the location of the flame must be moved along withthe motion of the hot gas, or the flame can fluctuate in intensity or beextinguished. A second source of vibration or a lever system is neededto keep the flame location in sync with the motion of the hot gas.

Colloids, Alloys, and the Like

Another application of embodiment of the present invention is rapidmixing of two or more immiscible fluids of different densities to createcolloids. As the vibration is increased, ripples form and grow at theinterface between the fluids, eventually becoming large enough thatbubbles of one fluid can be entrained in the other fluid. If thevibration was purely sinusoidal, the bubbles would tend to settle back,but when the vibration is non-sinusoidal as described above, bubbles ofthe right size can be levitated further into the other liquid. As thevibrations continue, larger bubbles break into smaller bubbles, untilthe aggregation rate (the rate that bubbles collide with each other andform large bubbles) substantially equals the rate that the vibrationsbreak up bubbles. A colloid can be quickly produced with a wide range ofvibration frequency, from a few cycles per seconds up to ultrasonicfrequencies. The colloid will persist as long as the vibration ismaintained. The frequency, shape, and amplitude of the vibration can beadjusted to change the size of the droplets, potentially making dropletssmall enough to maintain stability of the colloid long after thevibrations cease. Stabilizers can also be added to improve stability.

One example of this embodiment is in the production of ice cream andother frozen desserts. Cream, flavoring syrup, and air can be thoroughlymixed at room temperature and frozen afterwards. The colloid mixture canbe stable enough and fine-grained enough to be frozen slowly by storingthe container with the mixture in a freezer, with the result being asmoothly textured ice cream with small ice crystal grains. Thistechnique has several advantages over the traditional method of churningwhile cooling. First, the mixing device does not need to be cooled.Second, the container that the ice cream is mixed in can also be thecontainer that it is shipped and/or served or sold in, in which case noequipment cleaning is necessary between the manufacture of differentflavors. Freezing can even be done during delivery, such as in freezertrucks, and possibly delayed until after delivery, decreasing the riskof melting.

Another application is in the production of alloys or solidifiedcolloids that quickly separate after vibrations are stopped. Two or morefluids can be mixed into a fine colloid and vibrations continued duringa cooling process to solidify the mixture. The frequency and amplitudeof the vibrations can be adjusted to adjust the size of the grains ofthe different materials. This technique can be used to create new orimproved alloys, solid foams, and similar materials.

Fluidized Bed and Bubble Column Reactors

Compared to the flow rate of a fluidized bed reactor, an embodiment ofthe present invention can achieve higher velocity of particles relativeto the fluid. For a fluidized bed, there is one flow rate (or a narrowrange of rates) that fluidizes particles, but the vibration amplitudeand frequency of the present embodiment can be adjusted over a widerange, as the shape of the waveform can be adjusted to maintainlevitation. For example, the amplitude of the second harmonic can beadjusted relative to the first harmonic to achieve fluidization.Furthermore, embodiment does not require a recirculating path for thefluid.

Bubble column reactors, including water treatment applications, can alsobe improved or replaced with the embodiment. Researchers have found thatsinusoidal vibrations can increase mass transfer rates in bubble columnreactors. They have also noted that the rise of bubbles can be slowed bysinusoidal vibrations. They have not however, discovered how the rise ofbubbles can be completely stopped or even reversed throughnon-sinusoidal vibrations. Besides speeding up mass transfer rates,using non-sinusoidal vibrations to levitate the bubbles can increase theutilization of gas and allow the use of shorter bubble columns.

Vibration Testing

Vibration testing can also be improved with embodiments of the presentinvention. Current vibration testing standards only require sinusoidalvibrations, swept sine tests, random tests, and/or impulse tests.However, as shown above, significant effects can occur with periodic butnon-sinusoidal vibrations, even by adding just a second harmonic, thathas never been seen with a sinusoidal waveform or a random waveform.Vertical vibrations can cause particles to levitate in a less densefluid and even collect at the top, while horizontal vibrations can causehorizontal streaming, amongst other effects.

In particular, battery testing can be improved with embodiments thepresent invention. Batteries depend on a predictable, stable movement ofionic particles across an electrolytic fluid, and thus are particularlysensitive to vibrations that affect this movement. The need for thoroughvibration testing is even more important if the batteries will besubjected to external changes of pressure and/or temperature.Non-sinusoidal vibrations can cause damage that will not be exposedthrough any amount of sinusoidal or random vibration testing. Cavitationcan occur, especially if gas bubbles form inside the battery due to adrop in pressure, which can be caused by a drop in temperature. If thebattery container has a vent, vibrations or heat could cause the batteryto vent, dropping the pressure inside the battery, and, after cooling,vapor bubbles can form inside the battery. Non-sinusoidal vibrations canalso affect the flow of electrolyte, causing the concentration ofelectrolyte and ions to vary within the battery. Non-sinusoidalvibrations can also reduce or increase convection, which can cause thebattery to overheat. Vibration can also cause ion particles to flowfaster across the electrolyte solution, causing spikes in current.Non-sinusoidal vibrations can inhibit or increase ionic movement in onedirection, increasing or decreasing the current supplied or needed forcharging. Vibrations may also cause the electrolyte and ions to clumpdue to the effect of drafting. For all these reasons, it is preferableto vibration test lithium or other highly hazardous batteries using anon-sinusoidal waveform (such as the waveform in FIG. 3c composed of thefirst and second harmonic), while fluctuating temperature and pressureacross the full range that may be encountered in actual use.

In one embodiment, the vibration testing method includes several steps,which may be repeated for thoroughness or to check for long-termbehavior. The first step, which may be optional for some tests, is todecrease the pressure inside of the fluid environment so that vapor orgas bubbles are formed, or to make cavitation more likely in latersteps. This can often be accomplished simply by cooling the fluid (andkeeping the fluid cool through later steps) inside a sealed container.Alternatively, the container can be vented, the pressure reduced, andthe container can be resealed, with a small amount of gas bubblesallowed to replace some of the fluid. If the container under test has abuilt-in venting mechanism to reduce fluid in case high pressure buildsup inside the container (such as the vent on some lithium batteries),heating the fluid, vibrating the container, or reducing the pressureoutside of the vent, may reduce the pressure inside by forcing orsuctioning out some of the fluid inside the container. Then, thetemperature of the fluid can be returned to normal.

The next step in vibration testing is to vibrate the container over asufficient period of time with different sinusoidal and non-sinusoidalwaveforms along the axes of interest. In particular, at least three orfour different waveforms can be tested at each desired frequency. Alonga vertical (or partially vertical) axis, one waveform can besufficiently non-sinusoidal to cause the flow of small bubbles downwardand small heavier-than-fluid particles upwards. A waveform that is thesum of the first and second harmonics, as illustrated in FIG. 3, is oneembodiment. The same or similar waveform but inverted is anotherwaveform for testing. This waveform can inhibit the negative buoyancyeffect of sinusoidal vibrations on entrained bubbles, and prevent therise of heavier particles due to vibrations. Such a waveform can beimportant for testing the long-term effect of cavitation collapse.Entrained bubbles that sink due to the negative buoyancy effect ofsinusoidal vibrations on compressible bubbles may interfere or preventcavitation because those bubbles may grow and shrink from the pressurechanges, instead of the cavitation growth and collapse of new bubbles.(This is another reason why a pure sinusoid is not a preferred testwaveform by itself, as a sinusoid may cause only a brief amount ofcavitation at the initiation of the vibration, which will stop afterjust a few cycles once the entrained bubble has dropped to the bottomhalf of the fluid.) A third type of waveform for testing is one which isjust non-sinusoidal enough to levitate some bubbles or particlesthroughout the container. It may be desirable to modulate this waveformsomewhat to ensure a sufficiently wide range of levitation and mixing.Furthermore, different waveforms or amplitudes may be used to levitatedifferent types and sizes of particles or bubbles. Optionally,repetitive shock testing can also be performed, both upwards anddownwards, preferably at a sufficient amplitude to cause cavitation(although shock testing can be considered a subset of the non-sinusoidaltests already mentioned). Finally, a pure sinusoidal vibration can betested as well. Similar tests can be done on horizontal axes to test thepossibility that non-sinusoidal vibrations can bring about bulkmovement. Furthermore, horizontal vibration testing may be important forbatteries or other devices that have fluid sandwiched between solidvertical components or plates, as horizontal vibrations may affect therate of horizontal movement and diffusion of the fluid and particlesbetween the vertical plates.

In all these tests, the preferred waveform is the actual vibration ofthe innermost container containing the fluid, not the power applied tothe transducer or the vibration of the testing apparatus in the absenceof the test item or the vibration of any outer container. If thecontainer or fluid to be tested is part of a larger object, and it isnecessary or desirable to vibrate the larger object instead of thecontainer itself, then it may not be possible or practical to measure orknow the actual vibration waveform that the container experiences. Insuch a case, more waveforms can be tested, varying the phase and/oramplitude of the second harmonic (and possible higher harmonics) toensure that the inner container experiences all vibration waveforms ofinterest. For example, a single battery may contain several individualcells inside of an outer case, and it may be desirable to test theentire battery instead of the individuals cells to test the heatdissipation or other interactions between cells. If the cells are notfirmly attached to the outer case, the cells may vibrate with adifferently shaped waveform than the entire battery. Preferably anaccelerometer or audio transducer can be attached to the interior cellor cells and used as the reference waveform. If that is not possible,but the vibration response of the interior cells to the exterior batteryvibration is known, then the vibration of the battery can be adjusted toproduce the desired vibration of the internal cells. If the vibrationresponse is not known, then a variety of waveforms should be tested. Asuitable waveform can often be found by slowly sweeping the phase andamplitude of the second harmonic while looking for a non-linear responsefrom an acoustic transducer or other sensor that often indicatescavitation or other non-linear effects that can cause damage.

Tests can be repeated at different temperatures and pressures across theentire range of operation, particularly at lower temperatures andpressures, and the transition from one temperature and/or pressure toanother can increase the likelihood of cavitation, as explained above.

Each of the waveforms can be applied for a sufficient amount of time toallow for cumulative effects. Optionally, testing can also alternate orcycle through short periods of the different waveforms, to test whetherthe transitions cause damage or failure.

One embodiment includes an acoustic transducer or other sensor to detectacoustic waves caused by cavitation collapse or other non-linearresponse to the vibrations. In particular, cavitation and other effectsmay only occur at the initiation or end of application of each waveformor transitions between waveforms. The test procedures can make note ofany anomalies which can be evidence of cavitation collapse and thosetest conditions can be repeated to check for the accumulation of damage.

If the object to be tested is part of a larger system, it is preferredfor the testing to occur under conditions as close to normal operationas possible, and its performance under vibration compared to itsperformance without vibration. For example, if the test object is abattery, it is preferably tested within a circuit or charger thatsimulates normal usage, and the voltage and current waveforms whensubjected to vibrations can be compared to the waveforms withoutvibrations. After the test, the interior of the battery subjected tovibrations can be inspected against a battery that underwent the sametest without vibrations.

If damage from vibrations is found, then the object under test may beredesigned with internal or external vibration damping mechanisms.Alternatively, or in addition, a vibration sensor may be added to detectdangerous vibrations and/or the occurrence of cavitation collapse orother potentially damaging conditions. If pressure and/or temperaturevariations or other variables are also shown to take a role in the riskof failure, then those may be controlled and/or recorded by sensors.

Improving Batteries

Another object of the present invention is an apparatus, and method toincrease the current that a battery cell can supply, or the chargingspeed of a battery cell, through the application of sinusoidal ornon-sinusoidal vibrations. Horizontal sinusoidal vibrations increase theflow of electrolyte and ions between vertical electrodes, reducing theinternal resistance of the cell and increasing the maximum current, bothfor charging and discharging. Non-sinusoidal horizontal vibrations cancause ions to migrate in a specific direction. If the direction betweenthe cathodes and anodes is the same throughout the cell, such as in abipolar battery, then this migration may improve charging at the expenseof discharging, or vice-versa, depending on the polarity of thevibration waveform. A large enough vibration amplitude may even beenough to charge the cell or reduce the voltage required for charging.Vibration can be dynamically increased or decreased, or eliminatedentirely, depending on the current required. This flexibility allows alarger separation between electrodes, increasing safety by reducing riskof an internal short circuit and the ability to stop thermal runaway bystopping vibrations.

Ultrasound

Another application of the present invention is in the field of medicalultrasound. The shape of the ultrasound waveform can be adjusted toinduce streaming while keeping the risk of cavitation or tissue heatinglow. U.S. Pat. No. 5,523,058 (issued Jun. 4, 1996 to Shinichiro Umemura)disclosed an ultrasonic apparatus that combines the first and secondharmonic, but described the effect as increasing cavitation. Althoughcavitation may also be somewhat increased, much of their observed effectwas likely due to the streaming or mixing effect of non-sinusoidalvibrations on particles of different sizes, shapes, or densities. Addingodd harmonics instead of the second harmonic, at the proper phase andamplitude relationship (to approximate a square pressure wave, as anexample) may increase cavitation without causing streaming, unlesspassing through tissue or bubbles that have a sufficient non-linearresponse to the ultrasound. Conversely, adding harmonics with thecorrect phase and amplitude relationship, possibly by approximating atriangle pressure wave or the right polarity of a sawtooth wave, canreduce cavitation by reducing the maximum rate of change of pressure.Reducing the risk of cavitation may make ultrasound safer.

These same principles can be applied to the use of non-medicalultrasound. The ultrasonic waveform can be shaped and varied to controlthe amount of cavitation and the amount of mixing, streaming, andlevitation.

A further consequence of this invention is the realization that theremay be a need for a third metric for estimating the level of safety ofmedical ultrasound, in addition to the Thermal Index (TI), and theMechanical Index (MI). This new metric can provide a better measure ofthe likelihood of streaming and/or mixing caused by non-sinusoidalvibration, and can be computed from the amplitude of the second harmonic(or other even harmonics) measured in the reflected wave. Also, asadditional harmonics are added (or caused by non-linear response to asinusoidal wave), the definition of MI and possibly TI may be adjusted.

While the foregoing written description of the invention enables one ofordinary skill to make and use what is considered presently to be thebest mode thereof, those of ordinary skill will understand andappreciate the existence of variations, combinations, and equivalents ofthe specific embodiment, method, and examples herein. The inventionshould therefore not be limited by the above described embodiment,method, and examples, but by all embodiments and methods within thescope and spirit of the invention.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. The descriptions are not intended to limit the scope of theinvention to the particular forms set forth herein. Thus, the breadthand scope of a preferred embodiment should not be limited by any of theabove-described exemplary embodiments. It should be understood that theabove description is illustrative and not restrictive. To the contrary,the present descriptions are intended to cover such alternatives,modifications, and equivalents as may be included within the spirit andscope of the invention as defined by the appended claims and otherwiseappreciated by one of ordinary skill in the art. The scope of theinvention should, therefore, be determined not with reference to theabove description, but instead should be determined with reference tothe appended claims along with their full scope of equivalents.

What is claimed is:
 1. A method for estimating the level of safety ofultrasound equipment, the method comprising: measuring an amplitude of asecond or higher order harmonics in a reflected wave from the ultrasoundequipment.
 2. The method of claim 1, further comprising determining ifthe amplitude fits with a predetermined phase and amplituderelationship.
 3. The method of claim 2, further comprising adjusting theamplitude of the second or higher order harmonics if it does not fitwith the predetermined phase and amplitude relationship.
 4. The methodof claim 1, further comprising: adjusting a frequency of the reflectedwave, and causing an increase or decrease in cavitation based on thefrequency of the reflected wave.
 5. The method of claim 4, wherein theshape of the reflected wave can be varied to control the amount ofcavitation.